Five amazing night sky events for winter stargazers
Monday, December 7, 2015, 12:53 PM - Winter is right around the corner, and here are five events in our night sky that are definitely worth braving a little cold to see.
December - Watch the sky for naked-eye Comet Catalina
Starting this week, and until the middle of January, we have the opportunity to see a new visitor to the inner solar system. Comet C/2013 US10 (Catalina) - aka Comet Catalina - has emerged from behind the Sun, and is now visible in the predawn sky.
Seeing it this week will require very clear, very dark skies (see below), and will very likely require the assistance of binoculars, at the very least. Look above the eastern horizon, in the hour or so just before the sky starts to brighten.
Comet Catalina in the eastern sky, just before sunrise on December 1, 2015. Credit: Stellarium/S.Sutherland
There's some good news, though. The comet has already reached its closet point to the Sun, and is headed back towards the outer solar system, but two factors are going to make it easier to see.
The comet will rise earlier and earlier each day, and thus will be in darker skies as the days progress.
Earth is drawing closer to the comet as the planet swings around in its orbit. This means that Comet Catalina will continue to brighten throughout the month, and it will rise earlier and earlier with each morning, and thus be in darker skies for longer.
So, while it's just on the cusp of naked-eye visibility now (just below or at magnitude 6), it is expected to at least double in brightness by January. After the middle of January, the distance between Earth and the comet will grow, so we will quickly lose sight of it, although telescopes will still be able to see it until around the time it passes the orbit of Mars.
If you have ideal viewing conditions and a good telescope, here's what the comet looks like right now.
In this beautiful image - posted to Facebook by astrophotographer Fritz Helmut Hemmerich - the comet has two tails. The heavier dust tail points down and to the left, back along the comet's path. The lighter ion tail, visible as multiple streamers blowing off towards the upper right, points along the flow of the Sun's solar wind.
Discovered on October 31, 2013, by astronomers with the Catalina Sky Survey, was originally thought to be an asteroid, far out beyond the orbit of Jupiter. Subsequent observations revealed it to actually be a comet, and it appears to be on its one-and-only trip through our solar system.
This Oort Cloud comet was apparently orbiting our Sun somewhere in the interstellar space between here and Alpha Centauri, until it received some kind of nudge - either by a passing object or by bumping into some other Oord Cloud resident - that caused it to plummet into the Sun's gravity well. Now, having reached its closest distance to the Sun in the middle of November, and is on a trajectory that will take it back to interstellar space, very likely never to return.
Stay tuned for more information on this comet in the weeks to come!
December 7 - Conjunction of Venus and the Moon (and Comet Catalina!)
Back in October, a brilliant celestial triangle graced our skies, as Jupiter, Venus and Mars came very closer together from Earth's point of view. On the morning of December 7, from about 4 a.m. until sunrise, Venus will be rising with a very slim crescent moon in a close conjunction. Keep an eye on the pair around 6 a.m. and they will pass very close to Comet Catalina.
A conjunction of the crescent Moon with bright Venus on the morning of December 7. Credit: Stellarium/S.Sutherland
While Venus and the Moon will be visible from anywhere, as long as skies are clear of obscuring clouds, it will take ideal conditions to see Comet Catalina along with them.
December 13-14 - The peak of the Geminid meteor shower
Every year, in mid-December, Earth passes through a trail of space debris left behind by an object known as 3200 Phaethon. While identified as a roughly 5 km-wide asteroid, its unusual orbit - more similar to that of a comet than an asteroid - has earned 3200 Phaethon the nickname "rock comet" and NASA satellites have even spotted dust trails being blown off its surface as it passes around the Sun.
One mystery of this object and its meteor shower, though, is that the tiny amount of dust seen blowing off of 3200 Phaethon does not account for the abundance of meteors that flash through our atmosphere. It could be that this chunk of rock was broken off of a much larger object in the asteroid belt - perhaps main belt asteroid Pallas, according to NASA. If that's the case, most Geminid meteors could be debris that trailed behind 3200 Phaethon after the impact that broke it off from that larger body.
Regardless of its origin, when Earth encounters that dust stream each December, the tiny bits of rocky grit flying through the upper atmosphere create a particularly spectacular meteor shower in the night sky.
The position of the Geminids radiant in the eastern sky at 9 p.m. on the night of December 14, 2015. Credit: Stellarium/S.Sutherland
Under ideal conditions, stargazers can see up to 120 meteors per hour from this shower, and the rocky debris can produce a whole range of colours in these meteors. This is definitely one to bundle up for, so watch for updates as the date draws closer.
December 25 - Christmas Day Full Moon
Step out into the clear, brisk, pre-dawn air on December 25, 2015, turn to face the western horizon and you will see something that hasn't happened since 1977 and that won't happen again until 2034 - a Christmas Day Full Moon.
A Christmas morning Full Moon (exaggerated size in this simulated view, but it may look that big due to the "Moon Illusion"). Credit: Stellarium/S.Sutherland
Now, pick any day of the year and you'll find that there's a decade or more between two successive full moons on that particular date. So, there's really nothing particularly exceptional about this full moon. However, since it's very likely that many families will be up early on the morning of December 25, it's definitely a good chance to check this one out.
If you want to catch the exact moment of this full moon, be watching at exactly 11:12 UTC or 6:12 a.m. EST. This timing means that it will have likely already set in the eastern-most parts of Newfoundland, but given clear skies that morning, it should be visible for the rest of Canada.
January 3-4 - Peak of the Quadrantid meteor shower
The very first meteor shower of the new year is the Quadrantids, and it certainly starts off the year with the promise of a great show.
Since the radiant for this meteor shower is above the horizon all night long, stargazers need only wait until the sky becomes dark enough for the meteors to show up. There's a bit of a catch to this one, though.
Position of the Quadrantids radiant early in the morning of January 4, 2016. Credit: Stellarium/S.Sutherland
Unlike other meteor showers that tend to give at least a decent showing in the days before and after the peak, the Quadrantids peak is apparently very sharp. Thus, the night of January 3-4 is definitely the time to see this, and with the exact timing, it may be so sharp as to give Europe a slightly better show than North America.
Also, according to the International Meteor Organization (IMO), the number of meteors we can see from this shower varies from year to year. Back in 2008, it produced only around 80 meteors per hour. The year after that, it was more like 140 per hour. For a few hours on January 3, 2014, it apparently wow'd everyone by delivering over 200 meteors per hour, and there was a brief spike reported the next night when the rate jumped to over 300 per hour! Partly this variation is due to the weather (thus affecting how many people observe it and how many meteors they see), but it can also have to do with variations in the density of the debris stream. Overall, this meteor shower averages out at around 120 meteors per hour under ideal conditions - for someone under a very clear, very dark sky.
In an interesting coincidence, the Quadrantids not only produce about the same number of meteors as the Geminids, but these meteor showers both have similar origins. While the Geminids come from "rock comet" 3200 Phaethon, the parent body of the Quadrantids is an object known as 2003 EH1, an asteroid somewhere between 2.6-4.0 km wide, which is believed to be an "extinct comet" - what's left over after a comet loses most or all of its ice and volatile gases.
Best viewing, AKA "a clear, dark sky"
Time and time again you will see the phrase "clear, dark sky" or some variation, when it comes to watching meteor showers and other celestial events. What does this mean, and why does it matter?
As for the "clear" part, the weather will be a big factor when it comes to seeing any of these events from a specific location. Cloudy skies will make it impossible to see what's going on in the sky, and even high humidity can make it difficult to see anything, especially when you consider the next two factors.
When it comes to having a "dark sky" there are two things to consider.
The moon can easily spoil the show when it comes to some viewing events, especially meteor showers, and especially when it's near or at full moon. The amount of light the moon casts can easily overwhelm dim meteors, so that they go unnoticed by us here on the ground.
Possibly worse than the effects of the moon is light pollution, due to its insidious nature and the fact that we could actually control this, if we only took the time.
Many people who live in or near urban centres are disappointed when they go outside to see a meteor shower. Even when the sky is clear of clouds and the moon is nowhere to be seen, they still only spot one or two meteors, or perhaps none at all.
Since the majority of meteors are fairly dim – even during a very strong shower such as the Quadrantids – they can only be seen if there are no competing sources of light beyond just the stars.
Street lights, car lights, building lights, electronic signs, etc, all contribute as competition, and the bigger the urban centre, the more light it emits up into the atmosphere. Since this bright glow around cities is an unintended consequence (and certainly unwanted for anyone who wants an unobstructed view of the night sky), it is called light pollution.
For much of Canada, simply taking a short drive out of the city, town or village lights will result in a sky dark enough to see most of these events. However, southwestern Ontario and along the St. Lawrence Valley have some of the worst light pollution in all of Canada, as shown in the map below:
Any area shaded red, yellow or green, along with regions near them, is going to have at least some impact from this light pollution.
There are ways to control light pollution, mostly by changing the kinds of lights we use outdoors, and how we angle the light produced by them. These abatement methods typically result in lower costs, as well, as less electricity is used to power these lights. However, light pollution continues to be a problem.
There are some areas scattered about in these regions, known as Dark Sky Preserves, which are far enough away from city lights to allow good viewing conditions. Many astronomy clubs host events at these locations, even in winter, to give their members and the public the best chance at witnessing these amazing sites in our night sky.